It's all looking pretty good.The head needs to be stuck to the ground so the tail can do the bounce.The bit that catches my eye is the arc of many heads frame. Look at the spacing. Put the heads further apart as they get toward the ground = make the space between each head/eye greater as it gets closer to the ground. Also that frame is held for two frames. See what it looks like holding it for one frame.Immediately, on the frame after the head squashes into the ground, the tail should be going up. At the moment that reaction is delayed a bit too long.If you need to do something to the head, rather than have it stick to the ground, it can shudder. Every second frame make it a different shape applying the principle of stretch and squash.